VOL. III.] PHILOSOPHICAL TRANSACTIONS. 2QS 



adust drying of the sand, not able to afford any visible fumes fit for such a dis- 

 covery. I then proceeded to another way — to boil it in water, and having 

 poured that ofi\ to observe the alcali left after the water's evaporation. By 

 this means I discovered, that it abounded rather in sulphureous unctuousness, 

 than saline acrimony. Finding this, I applied first the quicksilver, mingled 

 with the ordinary magistrals, as they call them, used in that country, to curb 

 and break the force of these sulphureous impediments. But perceiving these to 

 be of no effect, I assisted the quicksilver with the caput mortuum of vitriol and 

 saltpetre, kept as a secret among the miners, but with as little signs of the 

 mercury's operation as before. Then I boiled my mixture over the fire, a way 

 found out in Peru in such difficult cases, but all to no purpose ; so froward a 

 matter it was, that it could not be brought to receive mercury, either by fair 

 means or by foul. Then I devised a way to torment it with a corrosive of or- 

 dinary separating water, impregnated with common salt, and it made a disso- 

 lution, like that of gold; which, thus dissolved, I showed to a mineralist, who 

 had been versed all his life-time in the separatory art of gold and silver; and he 

 would not believe but that it was true gold. But having steamed away the aqua 

 fortis, I found my hopes turned into a dirt something yellow, out of which, 

 with distilled vinegar, enforced with its own tartareous salt, I extracted a tinc- 

 ture more curious than useful. 



I shall only subjoin the grand use of mercury in separating silver in the 

 Indies, when that metal is generated, as commonly it is, in certain rocky stones, 

 abounding with bituminous and corrosive mixtures, so as to be impossible to 

 free it entirely from its corrupt matrix, by the violent way of melting, whatever 

 auxiliary ingredients may be added, as lead and artificial salts, and the like, be- 

 cause those sulphureous and vitriolic compounds, in the way of fusion, melting 

 together with the silver, sublime part of it away in a volatile fume by their 

 corroding acrimony, calcining and vitrif)'ing the other part, and robbing the 

 artificer of half his gain. In this case the use of quicksilver is found most ad- 

 vantageous, which is in this manner: Having reduced the ore into small pieces, 

 they calcine it first in a reverberating oven, yet with a moderate fire, for fear of 

 fusion, and driving away into the air part of the treasure ; this calcination serves 

 chiefly to free the mineral from what may hinder the operation of the quick- 

 silver; and it serves also to discover, by the colour of the fumes it yields, what 

 corrosive mixture chiefly abounds in it, besides that it renders the ore more 

 tractable and pliant under the mill-stone, which is to reduce it to a small flour 

 before the application of the mercury. This is chiefly used in those silver 

 veins that are hard and dry ; for such as are softer, abounding in oleaginous 

 sulphurs, before burning are first ground into powder in such mills as are often 



